In lifetime, subtype means longer lifetime (it's unintuitive). 'a : 'b means 'a is a subtype of 'b, which contains 'b and can be longer. Rust can improve this

In lifetime, subtype means longer lifetime (it's unintuitive). 'a : 'b means 'a is a subtype of 'b, which contains 'b and can be longer. Rust can improve this by introducing syntax like `'a contains 'b`